Tests: Add a way to configure custom options for FortranModules test

Read an undocumented cache entry to allow some CI builds to configure
this test in a special way.

Tests/CMakeLists.txt

@@ -3373,6 +3373,7 @@ ${CMake_BINARY_DIR}/bin/cmake -DDIR=dev -P ${CMake_SOURCE_DIR}/Utilities/Release
         --build-options ${build_options}
           -DCMake_TEST_NESTED_MAKE_PROGRAM:FILEPATH=${CMake_TEST_EXPLICIT_MAKE_PROGRAM}
           -DCMake_TEST_Fortran_SUBMODULES:BOOL=${CMake_TEST_Fortran_SUBMODULES}
+          ${CMake_TEST_FortranModules_BUILD_OPTIONS}
         )
       list(APPEND TEST_BUILD_DIRS "${CMake_BINARY_DIR}/Tests/FortranModules")
     endif()